The Broadcaster Edit
The Broadcaster is the person who transmits the video for SHawkins to receive. They seemingly create them from assets in the ECKVA database to directly target SH and to taunt them. They also appear to be represented by the person often dubbed as "The Doctor", the person-like entity with no mouth, eyes, or nose seen in ECKVA5, ECKVA6, and ECKVA7. SH also believes this to be the person who left them a pill of Preaxin.
The Broadcaster is also the same person who has been contacting viewers through the DScott3872 email address, and the Twitter formerly run by Jay and Tim of Marble Hornets.
Many speculate that the Broadcaster personally knew SH at some point in time, and that is the reason they're being so explicitly targeted.
Another popular theory is that this Broadcaster is the same person who appeared in Clear Lakes 44 Broadcast #11, given the aesthetic similarities between the two, and the early tweets from the beginning of the series.